Reliability of the FCR H-reflex

This study examined the intraclass reliability of the latency and amplitude of the Hoffmann reflex (H-reflex) in the flexor carpi radialis (FCR). The stability and consistency of the latency and peak-to-peak amplitude of the H-reflex were assessed across four test sessions. The FCR H-reflex was evoked in 39 volunteers (20 males and 19 females) on four separate days. The maximum amplitude of the motor response (Mmax) was determined each day and 10 responses were recorded at that stimulus intensity. The H-reflex was then evoked at an intensity corresponding to 5% of Mmax (H5%) and 10 recordings were obtained. The latency of the H-reflex and the peak-to-peak amplitude of both Mmax and H5% were calculated for each trial. Determination of reliability involves the consideration of both the stability and consistency of the measures. The reliability of the measures in this investigation was assessed using an analysis of variance and corresponding Lindquist intraclass correlation coefficient (ICC) model. In contrast to previous investigations, the H-reflex was evoked without facilitation in 95% (37/39) of the subjects tested. Statistical evaluation revealed that the latency and amplitude of the H-reflex, as well as the amplitude of Mmax, were both stable and consistent across the four test days. The ICC for Mmax was 0.97. The ICC for H5% was 0.92, and for latency of the H-reflex was 0.89. It was shown that the H-reflex can be easily evoked in the FCR and that the latency and amplitude of these recordings are highly reliable. The demonstration that the H-reflex can be easily and consistently evoked in the FCR has important clinical implications. It provides a tool for clinicians to assess the C7 level of the spinal cord and median nerve function.